The invention relates, in general, to the construction of relatively flexible elongated generally cylindrical members having reinforcing material in association with a substantial length of the cylindrical members to make the reinforced portions significantly less flexible than portions not having the reinforcing material associated therewith. In particular, the invention relates to catheters and the like, and methods of construction thereof, wherein a monolithic body has reinforcing material disposed in association with a portion thereof to render it less flexible than it inherently is, with the reinforcing material interrupted so that it does not extend for the entire length. The term "monolithic" as used in the present specification and claims means completely integral, as opposed to two-piece constructions which are common in the prior art.
In the construction of catheters for many functions, particularly electrode catheters or catheters used to inject radiopaque materials into body structures, it is essential that some portions of the catheter be soft and flexible. However, in order to properly position the catheter in the patient's body, it is necessary for other portions of the catheter to be stiff. These two conflicting requirements are usually accommodated in the prior art by making the tip of the catheter (and/or portions thereof that must be bent significantly in use or in insertion) so that it is soft and flexible, while the rest of the catheter is stiff. For instance U.S. Pat. No. 3,485,234 to Stevens shows a typical prior art catheter, and method of construction thereof, wherein a portion of a reinforced catheter body is ground off to expose a small portion of the wire braid reinforcement, and a separate and distinct tip of flexible material is slipped over the ground off end and fused to the catheter body by heat and pressure. Catheters constructed in this manner are not entirely suitable since the parts that are fused together can disassociate within the patient's body, with disastrous consequences, and additionally such catheters are relatively difficult to produce. In U.S. Pat. No. 4,321,226 it is suggested that a tubular catheter can be constructed by applying the reinforcing material to the entire catheter body, and after application to the catheter body selectively grinding off portions of the reinforcement. This procedure is relatively difficult to implement, and results in disruption of the reinforcement and marring of the core and results in surfaces that are not in dimensional tolerance and are not smooth. Even when an over-extrusion is applied the catheter may not have the desired dimensional tolerance or smoothness.
These disadvantages of prior art catheters, and methods of construction, are avoided by providing a monolithic construction according to the present invention.
According to one aspect of the present invention, a generally cylindrical member, such as (but not restricted to) a catheter, cannulae, or the like, is provided consisting of a relatively flexible elongated monolithic generally cylindrical body, and reinforcing material in association with a significant length of the cylindrical body, the reinforcing material making the body portions with which it is associated significantly less flexible, but a portion of the monolithic body being free of reinforcing material and thus retaining its relative flexibility. The cylindrical body may be hollow (e.g. a biological catheter) or solid (e.g. an electrode catheter), and preferably is made of a bio-compatible thermoplastic material.
The reinforcing material preferably comprises strands wrapped around the circumference of an inner core portion of the cylindrical body. Typical materials of which the strand may be formed include metal wire (e.g. steel wire), or synthetic fibers (e.g. fiberglass or aramid). The wrapping of the body by the strands may be accomplished by braiding, helical wrapping, or in a wide variety of other conventional reinforcing manners.
While any portion along the length of the member may be free of reinforcing material, for many medical uses it is desirable that the tip of the member be relatively soft and flexible, and thus the tip portion is free of reinforcing material.
According to another aspect of the present invention, a method is provided for constructing a reinforced monolithic elongated generally cylindrical member. The method comprises the steps of: (a) Forming a generally cylindrical monolithic body of relatively soft material, so that the body is relatively flexible; and (b) Disposing reinforcing material in operative association with a portion, but not all, of the body along the length thereof, so that where the reinforcing material is applied the member constructed is significantly less flexible than the body, but where the reinforcing material is not applied the member retains substantially the same flexibility as the body. Step (a) of the method according to the invention may be practiced by forming either a hollow or solid core of thermoplastic material, and step (b) is practiced by passing the inner core through a conventional reinforcement wrapping (e.g. braiding) machine. The wrapping operation is terminated at predetermined intervals for predetermined periods of time, and while the wrapping operation is terminated the body is continuously fed so that straight lengths of reinforcing strands are disposed on the periphery of the body. The body, with reinforcing strands, passes through a heated die so that the wrapped strands (e.g. braids) adhere to the surface of the body, but the straight portions do not. The straight portions then pass through a strand cutting mechanism, such as a mechanical cutting mechanism, at which point the straight portions are cut off. The member may then pass to an over extruder, and eventually is cut to length, the reinforcement-free portions of the monolithic catheter produced providing the desired flexibility for use and/or insertion of the catheter, and/or providing a tip portion that will not damage internal organs or the like. The member is produced without the necessity of forming the reinforcement braids over the entire length with subsequent grinding off of the unused portions.
It is the primary object of the present invention to provide a simple and effective generally cylindrical member, and method of construction thereof, having a relatively flexible elongated monolithic generally cylindrical body with reinforcing material disposed in operative association with a portion, but not all, of the length of the member. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and the appended claims.